By adjusting the addition time of palladium nanoparticles, during the formation of ZIF-8, an efficient and facile method was proposed to control the palladium spatial distribution within ZIF-8 crystals. Characterizations reveal that the addition time can significantly affect the particle size of Pd@ZIF-8 and palladium spatial distribution. As the PVP-stabilized palladium nanoparticles are added at the early stage of the ZIF-8 formation, larger ZIF-8 crystals with completely embedded palladium nanoparticles can be obtained. Introducing the PVP-stabilized palladium nanoparticles later can lead to the formation of smaller ZIF-8 crystals with all the palladium nanoparticles on the outer surfaces of ZIF-8. The catalytic performance of Pd@ZIF-8 strongly depends on the palladium spatial distribution, and the Pd@ZIF-8 with completely embedded palladium nanoparticles can provide excellent product selectivity and better catalytic stability in the hydrogenation of alkenes. (C) 2016 Elsevier B.V. All rights reserved.